Composite resin molded article

ABSTRACT

A composite resin molded article includes: a base resin; and fillers dispersed in the base resin, wherein the fillers include fibrous fillers and particulate fillers having aspect ratios lower than aspect ratios of the fibrous fillers.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority of Japanese Patent Application No.2018-157633 filed on Aug. 24, 2018, the contents of which isincorporated herein by reference.

BACKGROUND 1. Technical Field

The present disclosure relates to a composite resin molded article whichmakes it possible to achieve a molded article excellent in mechanicalproperties.

2. Related Art

So-called “general-purpose plastics” such as polyethylene (PE),polypropylene (PP), polystyrene (PS), polyvinyl chloride (PVC) are notonly considerably inexpensive but also easy to form, and has a weight aslow as a small fraction of a weight of a metal or a ceramic. For thisreason, the general-purpose plastics are often used as materials forvarious livingwares such as bags, various packages, various containersand sheets, and also as materials for industrial components such asautomotive components and electrical components, daily commodities,miscellaneous goods and the like.

However, the general-purpose plastics have drawbacks such asinsufficient mechanical strength. For this reason, the general-purposeplastics do not have sufficient properties required for materials usedfor various industrial products including machine products such asautomobiles, and electric/electronic/information products, and thecurrent state is that the application range of the general-purposeplastics is restricted.

On the other hand, so-called “engineering plastics” such aspolycarbonate, fluorine resin, acrylic resin and polyamide are excellentin mechanical properties, and are used for various industrial productsincluding machine products such as automobiles, andelectric/electronic/information products. However, the engineeringplastics have problems such as high price, difficulty in monomerrecycling, and high environmental load.

Thus, it is demanded to significantly improve the material properties(mechanical strength and the like) of the general-purpose plastics.There is known a technology to improve a mechanical strength of ageneral-purpose plastic by dispersing a natural filler, a glass fiber, acarbon fiber or the like as a fibrous filler in a resin of thegeneral-purpose plastic for the purpose of strengthening thegeneral-purpose plastic. Also there is known a technology to improve amechanical strength of a general-purpose plastic by dispersing aninorganic powder such as talc and silica, a cellulose-based powder suchas pulp powder, waste paper powder and wood chips, or the like as aparticulate filler in a resin of the general-purpose plastic. Above all,organic fillers such as cellulose have attracted attention asreinforcing materials because of inexpensiveness and excellentenvironmental properties in disposal.

Various companies have proceeded with studying in order to improve themechanical strength of the general-purpose plastics. In Japanese PatentNo. 3500403, as shown in FIG. 5, a cellulose-based powder 53 whichpasses through a 10 mesh having an aspect ratio of 2 or higher and doesnot pass through a 60 mesh is added to a resin 51 to enhance an impactstrength.

SUMMARY

In Japanese Patent No. 3500403, the cellulose-based powder 53 whichpasses through a 10 to 60 mesh i.e. a mesh with an opening width of 300μm to 1.6 mm is used to provide a composite resin having a high impactstrength and an excellent appearance. As shown in FIG. 5, the compositeresin has a low elastic modulus because the filler is composed of onlythe powder. Although the elastic modulus is improved by making thefiller fibrous, there has been a problem that the impact strength islowered and therefore it is difficult to achieve both the elasticmodulus and the impact strength. Moreover, there has been a problem thataggregates of the filler are increased by adding the fibrous filler, andtherefore the appearance is impaired.

One non-limiting and exemplary embodiment provides a composite resinmolded article having a high elastic modulus, a high impact resistance,and a good appearance.

In one general aspect, the techniques disclosed here feature: acomposite resin molded article includes:

a base resin; and

fillers dispersed in the base resin

wherein the fillers include fibrous fillers, and particulate fillershaving aspect ratios lower than aspect ratios of the fibrous fillers.

The composite resin molded article according to the present disclosuremakes it possible to achieve a composite resin molded article having ahigh elastic modulus and a high impact resistance and excellent inappearance.

Additional benefits and advantages of the disclosed embodiments will beapparent from the specification and figures. The benefits and/oradvantages may be individually provided by the various embodiments andfeatures of the specification and drawings disclosure, and need not allbe provided in order to obtain one or more of the same.

BRIEF DESCRIPTION OF DRAWINGS

The present disclosure will become readily understood from the followingdescription of non-limiting and exemplary embodiments thereof made withreference to the accompanying drawings, in which like parts aredesignated by like reference numeral and in which:

FIG. 1 is a schematic sectional drawing of a composite resin moldedarticle in a first embodiment;

FIG. 2A is a schematic drawing of a fibrous filler in the firstembodiment;

FIG. 2B is a partial enlarged view of an end part of the fibrous fillerin FIG. 2A;

FIG. 3 is a schematic diagram of a production process for the compositeresin molded article in the first embodiment;

FIG. 4 is a table showing measurement results in examples 1 to 3 andcomparative examples 1 to 8; and

FIG. 5 is a schematic sectional drawing of a composite resin moldedarticle in Japanese Patent No. 3500403.

DETAILED DESCRIPTION

Hereinafter, a composite resin molded article according to theembodiment will be described with reference to the drawings. In thefollowing description, for the same constituents, the same symbols areprovided, and the explanation for the identical constituent isappropriately omitted.

First Embodiment

FIG. 1 is the schematic sectional drawing of the composite resin moldedarticle 10 according to a first embodiment. FIG. 2A is the schematicdrawing of a fibrous filler 2 in the first embodiment. FIG. 2B is thepartial enlarged view of the end part A of the fibrous filler 2 in FIG.2A.

The composite resin molded article in the first embodiment is made of amelt-kneaded material containing a base resin, fillers and a dispersant.The fillers include fibrous fillers and particulate fillers. In thecomposite resin molded article, the fibrous fillers 2 having a highaspect ratio and the particulate fillers 3 having a low aspect ratio aredispersed in a base resin 1, as shown in the schematic sectional drawingof FIG. 1

In the first embodiment, the base resin 1 is preferably a thermoplasticresin for securing good moldability. Examples of the thermoplastic resininclude an olefin-based resin (including a cyclic olefin-based resin), astyrene-based resin, a (meth)acrylic resin, an organic acid vinylester-based resin or a derivative thereof, a vinyl ether-based resin, ahalogen-containing resin, a polycarbonate-based resin, a polyester-basedresin, a polyamide-based resin, a thermoplastic polyurethane resin, apolysulfone-based resin (polyether sulfone, polysulfone, etc.), apolyphenylene ether-based resin (a polymer of 2,6-xylenol, etc.), acellulose derivative (cellulose esters, cellulose carbamates, celluloseethers, etc.), a silicone resin (polydimethylsiloxane,polymethylphenylsiloxane, etc.), rubber or elastomer (a diene-basedrubber such as polybutadiene and polyisoprene, a styrene-butadienecopolymer, an acrylonitrile-butadiene copolymer, an acrylic rubber, anurethane rubber, a silicone rubber, etc.), and the like. The resinsdescribed above may be used alone or in combination. Note that the baseresin 1 is not limited to the aforementioned materials as long as thebase resin 1 is thermoplastic.

Among these thermoplastic resins, the olefin-based resin having arelatively low melting point is preferable as the base resin 1. Theolefin-based resin includes not only a homopolymer of an olefin-basedmonomer but also a copolymer of olefin-based monomers and a copolymer ofan olefin-based monomer and another copolymerizable monomer. Examples ofthe olefin-based monomer include acyclic olefins (an α-C2-20 olefin suchas ethylene, propylene, 1-butene, isobutene, 1-pentene,4-methyl-1-pentene, and 1-octene), cyclic olefins, and the like. Theseolefin-based monomers may be used alone or in combination. Among theolefin-based monomers, the acyclic olefins such as ethylene andpropylene are preferable. Examples of other copolymerizable monomersinclude a fatty acid vinyl ester such as vinyl acetate and vinylpropionate; a (meth)acrylic monomer such as (meth)acrylic acid, alkyl(meth)acrylate and glycidyl (meth)acrylate; an unsaturated dicarboxylicacid such as maleic acid, fumaric acid and maleic anhydride, or ananhydride thereof; a vinyl carboxylate (e.g. vinyl acetate, vinylpropionate, etc.); a cyclic olefin such as norbornene andcyclopentadiene; a diene such as butadiene and isoprene, and the like.These copolymerizable monomers may be used alone or in combination.Specific examples of the olefin-based resin include copolymers ofacyclic olefins (especially α-C2-4 olefin) such as a polyethylene (lowdensity, medium density, high density or linear low densitypolyethylene, etc.), a polypropylene, an ethylene-propylene copolymer,and a ternary copolymer such as ethylene-propylene-butene-1, and thelike.

Next, the dispersant will be described. The composite resin moldedarticle in the present embodiment may contain a dispersant for thepurpose of improving adhesiveness among the fibrous fillers 2, theparticulate fillers 3 and the base resin 1, dispersibility of thefibrous fillers 2 and the particulate fillers 3 in the base resin 1, orthe like. Examples of the dispersant include various titanate-basedcoupling agents, silane coupling agents, a modified polyolefin graftedwith an unsaturated carboxylic acid, a maleic acid, a maleic anhydrideor an anhydride thereof, a fatty acid, a fatty acid metal salt, a fattyacid ester, and the like. Preferably, the silane coupling agent is of anunsaturated hydrocarbon type or an epoxy type. The dispersant has noproblem even if the surface of the dispersant is modified by treatmentwith a thermosetting or thermoplastic polymer component. In the presentembodiment, a content of the dispersant in the composite resin moldedarticle is preferably 0.01% by mass to 20% by mass, more preferably 0.1%by mass to 10% by mass, and even more preferably 0.5% by mass to 5% bymass. When the content of the dispersant is less than 0.01% by mass, thedispersion is impaired, meanwhile when the content of the dispersant ismore than 20% by mass, the strength of the composite resin moldedarticle is lowered. The dispersant is appropriately selected dependingon the combination of the base resin 1, the fibrous fillers 2 and theparticulate fillers 3, and may not be added in the case that thedispersant is not required.

Next, the fibrous fillers 2 and the particulate fillers 3 will beexplained. In the particulate fillers 3, the material is basically thesame as that of the fibrous fillers 2, and only the aspect ratio isdifferent from that of the fibrous fillers 2. Thus, in the followingdescription, the fibrous fillers 2 will be explained in detail. In thepresent embodiment, the fibrous fillers 2 (hereinafter simply referredto as “fiber” in some cases) contained in the composite resin moldedarticle is used mainly for the purpose of improving a mechanicalproperty, improving a dimensional stability by decreasing a linearexpansion coefficient, or the like, in the resin molded article moldedusing the composite resin molded article. For this purpose, the fibrousfillers 2 preferably have an elastic modulus higher than of the baseresin 1, and specific examples of the fibrous fillers 2 include a carbonfiber (carbonous fiber), a carbon nanotube, pulp, cellulose, a cellulosenanofiber, lignocellulose, a lignocellulose nanofiber, a basic magnesiumsulfate fiber (magnesium oxysulfate fiber), a potassium titanate fiber,an aluminum borate fiber, a calcium silicate fiber, a calcium carbonatefiber, a silicon carbide fiber, wollastonite, xonotlite, various metalfibers, a natural fiber such as cotton, silk, wool and hemp, a jutefiber, a regenerated fiber such as rayon and cupra, a semisyntheticfiber such as acetate and promix, a synthetic fiber such as polyester,polyacrylonitrile, polyamide, aramid and polyolefin, as well as amodified fiber obtained by chemically modifying a surface and a terminalof any of the aforementioned fibers, and the like. Above all, thecarbons and celluloses are particularly preferable from the viewpointsof availability, high elastic modulus, and low linear expansioncoefficient. Furthermore, the cellulose natural fibers are preferablefrom the viewpoint of environmental properties.

Shapes of the fibrous fillers 2 and the particulate fillers 3 will beexplained. The symbol L represents a length of the fibrous filler 2 orthe particulate filler 3 (hereinafter referred to as “fiber length” insome cases), and the symbol d represents a width of the fibrous filler 2or the particulate filler 3 (hereinafter, referred to as “fiberdiameter” in some cases). In relation to the fibrous fillers 2 and theparticulate fillers 3, when a content of the fibers having a high aspectratio (L/d) is large i.e. when a content of the fibrous fillers 2 islarge, the elastic modulus is improved. The aspect ratios of the fibrousfillers 2 are preferably 10 or higher. However, when the content of thefibers having high aspect ratios is large, the impact resistance isdeteriorated, furthermore the fiber aggregates increase, and theappearance is impaired. On the other hand, when the content of thefibers having low aspect ratios is large i.e. when the content of theparticulate fillers 3 is large, the impact resistance is improved, thefiber aggregates decrease, and also the appearance is good. The aspectratios of the particulate fillers 3 are preferably 2 or lower. However,when the content of the fibers having low aspect ratios is large, theelastic modulus is lowered.

The relationship between the aspect ratio and the elastic modulus willbe described. When the composite resin molded article is loaded withstress, if there are fibers having high aspect ratios, the compositeresin is not distorted because the resin stretches but the high rigidityfibers hardly stretch. Thereby, the elastic modulus is improved. On theother hand, in the case of the fibers having low aspect ratios, adistortion-suppressing effect of the fibers is reduced when loaded withthe stress, the composite resin is distorted, and the elastic modulus islowered.

The relationship between the aspect ratio and the impact resistance willbe described. When the composite resin molded article is loaded withimpact, if there are fibers having high aspect ratios, the fibers cannotfollow elongation of the resin, so that a crack is generated between theresin and the fiber, and the crack as a starting point leads tobreakage. On the other hand, in the case of the fibers having low aspectratios, the fibers follow elongation of the resin owing to the finefibers when loaded with the impact, so that a crack is hardly generated,and the composite resin molded article is hard to break.

The relationship between the aspect ratio and the appearance will bedescribed. The fibers having high aspect ratios i.e. the fibrous fillersand the fibers having low aspect ratios i.e. the particulate fillers arekneaded together, so that the fibers having low aspect ratios i.e. theparticulate fillers are inserted between the fibers having high aspectratios i.e. the fibrous fillers, aggregation is suppressed, and theappearance is improved.

As described above, it is preferable that the fibers having high aspectratios (fibrous fillers) and the fibers having low aspect ratios(particulate fillers) are mixed in the composite resin molded articlefrom the viewpoints of the elastic modulus, the impact resistance, andthe appearance. Simulation calculates what relation of the mixing ratioof each fiber improves the property. It is preferable that an abundanceratio of fibers having aspect ratios of 10 or higher is 1% to 10%, andan abundance ratio of fibers having aspect ratios of 2 or lower is 50%to 70%. In other words, it is preferable that a ratio of the fibrousfillers in the fillers is 1% to 10%, and a ratio of the particulatefillers in the fillers is 50% to 70%.

In addition, an abundance ratio of other fibers having aspect ratios ofhigher than 2 and lower than 10 is 20% to 49%.

In addition, the aforementioned abundance ratio refers to a ratio ofeach number of the fibrous fillers, the particulate fillers and theother fillers in the total number of the fillers.

Hereinbefore, the state of the mixed fibers having different aspectratios has been described, and hereinafter the state of the fibersexisting in the composite resin molded article will be described. Asdescribed above, it has been described that the fibers having highaspect ratios (fibrous fillers) increases the elastic modulus, and thefibers having low aspect ratios (particulate fillers) improves theimpact resistance. In view of the composite resin molded article, alarge number of fibers having high aspect ratios of 10 or higher may becharged at the surface layer of the composite resin molded article, andfibers having low aspect ratios of 2 or lower may be charged at the coreside of the composite resin molded article. In this case, since theelastic modulus at the surface layer side is high, a rigidity of theentire composite resin molded article is increased, and the impact canbe absorbed at the core side of the composite resin molded article onthe impact loading, and also the impact resistance is improved. For thisreason, it is preferable that a large number of fibers having highaspect ratios of 10 or higher are charged at the surface layer of thecomposite resin molded article, and fibers having low aspect ratios of 2or lower are charged at the core side of the composite resin moldedarticle. Herein, as shown in FIG. 1, when a thickness of the compositeresin molded article 10 is represented by T and a distance from thesurface of the composite resin molded article 10 is represented by TF,the “surface layer of composite resin molded article” refers to a partwhere e.g. TF 0.2×T is satisfied. In addition, the “core side ofcomposite resin molded article” refers to a part where e.g. TF>0.2×T issatisfied. Note that the “surface layer of composite resin moldedarticle” is present at both the front side and the back side of thecomposite resin molded article 10, as shown in FIG. 1.

When a composite resin pellet is applied to a part to be colored in aplurality of colors including white, such as white goods, colorabilityis required for the fibrous filler composite resin. Whiteness of thecomposite resin molded article should be maintained for providingcolorability for the composite resin molded article, and thus whitenessof fibers to be added should be maintained. Lightness of L valuedetermined by a color difference measurement of the fiber is preferablyhigh. Lightness of L value of the fiber for improving a coloring degreeof the composite resin molded article has been experimentallycalculated, and the L value is preferably higher than 80, morepreferably 85 or higher.

States of the fibers in the composite resin molded article will bedescribed. The whiteness at the surface layer side of the compositeresin molded article is preferably high for improving the colorabilityfor the composite resin molded article. Thus, the composite resin moldedarticle has lightness of different L values determined by the colordifference measurement in the cross-sectional direction, and it ispreferable that lightness of the L value at the surface layer side ishigher than lightness of the L value at the core side.

For further improving the mechanical properties, specific surface areasof the fibers are preferably large because a larger bonded interfacebetween the fibers and the base resin leads to improvement of theelastic modulus. For increasing the specific surface areas of thefibers, a structure that at least one end part A in the fiber lengthdirection is partially defibrated in one fiber as shown in FIG. 2A andFIG. 2B is most preferable. In FIG. 2B, the symbol 4 represents thedefibrated part. The optimum shape of the fiber is calculated fromexperiments and simulation results as follows. Preferably, thedefibrated part 4 has a length of 5% to 50% of the fiber length L of theentire fibrous filler 2. If the length of the defibrated part 4 is lessthan 5% of the total fiber length L, the elastic modulus is not improvedbecause of the small specific surface area, and if the length of thedefibrated part 4 is not less than 50% of the total fiber length L, thedefibrated part 4 having a high aspect ratio is dominant, therefore thefibers are easy to orientate during injection molding, and the impactstrength is decreased.

Next, the characteristics of the fibrous fillers 2 will be explained.The types of the base resin 1 and the fibrous fillers 2 are as describedabove, but if the fibrous fillers 2 are too soft relative to the baseresin 1 i.e. the elastic modulus is low, the entire composite resinmolded article has a low elastic modulus, and as a result, the strengthis lowered. On the other hand, if the fibrous fillers 2 are too hardrelative to the base resin 1 i.e. the elastic modulus is high, a shockwave caused by impact does not propagate but is absorbed at theinterface between the base resin 1 and the fibrous fillers 2, thereforecracks and crazes are easily caused near the interface, and as a result,the impact resistance is lowered. As for the relationship of the elasticmodulus between the base resin 1 and the fibrous fillers 2, the elasticmodulus of the fibrous fillers 2 is higher, and the differencetherebetween is preferably made as small as possible. The optimalrelationship is calculated from the simulation results, and thedifference in the elastic modulus between the base resin 1 and thefibrous fillers 2 is preferably not more than 20 GPa.

In addition, for these fibrous fillers 2, a filler having a surfacetreated with various titanate-based coupling agents, silane couplingagents, a modified polyolefin grafted with an unsaturated carboxylicacid, a maleic acid, a maleic anhydride or an anhydride thereof, a fattyacid, a fatty acid metal salt, a fatty acid ester, or the like may beused for the purpose of improving the adhesiveness with the base resin 1or the dispersibility in the composite resin molded article.Alternatively, a filler having a surface treated with a thermosetting orthermoplastic polymer component may be used with no problem.

Next, a production method will be described. FIG. 3 is a flow chartillustrating the production process for the composite resin moldedarticle in the first embodiment.

(1) A base resin, fibrous fillers also including particulate fillers,and if necessary, a dispersant are put into the melt-kneading apparatus,and melt-kneaded in the apparatus. Thereby, the base resin is melted,and the fibrous fillers and the dispersant are dispersed in the meltedbase resin. At the same time, the shearing action of the device promotesdefibration of an aggregate of the fibrous fillers, and the fibrousfillers can be finely dispersed in the base resin.

Conventionally, fibrous fillers and particulate fillers obtained bypreviously defibrating fibers through a pretreatment such as wetdispersion have been used. However, if the fibrous fillers arepreviously defibrated in a solvent used in the wet dispersion, thefillers are more likely to be defibrated than in the melted base resin,and therefore it is difficult to defibrate only the end part, resultingin a state that the entire fibrous filler is defibrated. In addition,there have been problems that the number of processes is increased byadding the pretreatment, and the productivity is deteriorated.

In contrast, in the production process of the composite resin moldedarticle in the present embodiment, the fillers are melt-kneaded togetherwith the base resin, the dispersant and the like (all-dry process)without the pretreatment by wet dispersion intended to defibrate andmodify the fibrous fillers and particulate fillers. In this process, thewet dispersion treatment of the fibrous filler is not carried out, sothat the fibrous filler can be partially defibrated only at the end partas described above, furthermore the number of processes is small, andthe productivity can be improved.

For preparing the fiber in the form according to the present disclosureby the all-dry process, it is preferable to apply a high shearig stressduring kneading. Specific examples of the kneading implement include asingle-screw kneader, a twin-screw kneader, a roll kneader, a Banburymixer, a combination thereof, and the like. A continuous twin-screwkneader and a continuous roll kneader are particularly preferable fromthe viewpoints of easy application of high shear and a high massproductivity. A kneading implement other than the aforementionedimplements may be used as long as the implement can apply a high shearstress.

(2) The composite resin molded article extruded from the melt-kneadingapparatus is formed into a pellet shape through a cutting process usinga pelletizer or the like. Examples of the pelletization method includean in-air hot cut method, an in-water hot cut method, a strand cutmethod, and the like, which are carried out immediately after the resinmelting. Alternatively, a pulverization method, in which after once amolded article or a sheet is formed, the molded article or the sheet ispulverized and cut, and the like is also included.

This pellet is injection-molded, and thereby an injection-molded articleas the composite resin molded article can be prepared. When the fibrousfillers and the particulate fillers in the pellet are mixed as describedabove, an injection-molded article excellent in elastic modulus, impactresistance and appearance can be obtained. Hereinafter, each example andeach comparative example in experiments carried out by the inventorswill be explained.

EXAMPLE 1

A pulp-dispersed polypropylene composite resin molded article wasproduced by the following production method.

As a starting material for the fibrous fillers and particulate fillers,a coniferous pulp (trade name: NBKP Celgar, manufactured by MitsubishiPaper Mills Limited.) was used. The coniferous pulp was pulverized by apulverizer to obtain a mixture of the fibrous fillers and theparticulate fillers. An aspect ratio of each filler was adjusted in thepulverization process. A polypropylene as a base resin (trade name:J108M, manufactured by Prime Polymer Co., Ltd.), a mixture of thefibrous fillers and particulate fillers, and a maleic anhydride as adispersant (trade name: UMEX, manufactured by Sanyo Chemical Industries,Ltd.) were weighed out so that a weight ratio was 85:15:5, and they weredry-blended. Subsequently, the mixture was melt-kneaded and dispersed bya twin-screw kneader (KRC kneader manufactured by Kurimoto, Ltd.). Theshearing force can be changed by changing the configuration of the screwin the twin-screw kneader. The specification in example 1 was of themedium shear type. The resin melt was thermally cut to prepare apulp-dispersed polypropylene pellet.

A test piece of the composite resin molded article was produced by aninjection molding machine (180AD, manufactured by THE JAPAN STEEL WORKS,LTD.) using the prepared pulp-dispersed polypropylene pellet. In thecondition for preparing the test piece, a resin temperature was 190° C.,a mold temperature was 60° C., an injection speed was 60 mm/s, and afollow-up pressure was 80 Pa. The shape of the test piece was changeddepending on evaluation items described below, a No. 1-sizedumbbell-shaped test piece was prepared for measuring an elasticmodulus, and a 60 mm square flat plate having a thickness of 1.6 mm wasprepared for testing the drop impact and checking the appearance. Inaddition, in order to evaluate the colorability, the composite resinmolded article of the flat plate was prepared by dry-blending thecolorant during molding. The test piece of the obtained pulp-dispersedpolypropylene composite resin molded article was evaluated by thefollowing method.

(Aspect Ratio and End Defibrating Property of Fiber)

The obtained pulp-dispersed polypropylene pellet was immersed in axylene solvent to dissolve the polypropylene, and shapes of remainingpulp fibers were observed by SEM. About 50 representative fibers weremeasured at five sites of each fiber, and as a result, a percentage ofthe fibers having aspect ratios of 10 or higher was 5 to 10%, and apercentage of the fibers having aspect ratios of 2 or lower was 50 to60%. The end parts of the fibers were in a defibrated state.

(Color Difference L Value of Fiber)

Pulp fibers were put into a cup up to a full level, the top of the cupwas flattened, the color difference was measured using acolor-difference meter (Chroma Meter CR-400, manufactured by KONICAMINOLTA JAPAN, INC.). As a scale of whiteness, lightness of L value wasused. The L value was 90.

(Aspect ratios of fibers at surface layer side and core side of resin,and color difference L values)

The surface layer side and the core side of the composite resin moldedarticle were separated from each other by cutting, and each fiber aspectratio and each color difference L value were compared as describedabove. The aspect ratios of the fibers at the surface layer side werehigher than at the core side. The color difference L value at thesurface layer side was higher than at the core side.

(Elastic Modulus of Composite Resin Molded Article)

A tensile test was performed using the obtained No. 1 dumbbell-shapedtest piece. Herein, as a method for evaluating an elastic modulus, avalue of lower than 1.7 GPa was expressed as “Bad”, a value of 1.7 GPaor higher and lower than 2.1 GPa was expressed as “Middling”, and avalue of 2.1 GPa or higher was expressed as “Good”. The test piece hadan elastic modulus of 2.2 GPa, and was rated as “Good”.

(Result of Drop Test of Composite Resin Molded Article)

A drop impact test was carried out using the obtained flat test piece.Specifically, 250 g of plumb bob was dropped from a height of 80 cm tothe plate surface of the test piece, and it was confirmed whether acrack was generated. In this evaluation method, a test piece showing nocrack was expressed as “Good”, a test piece showing a crack having alength of shorter than 10 mm only on a surface was expressed as“Middling”, a test piece showing a through crack or a crack having alength of 10 mm or longer was expressed as “Bad”. The test piece did notshow any crack, and was rated as “Good”.

(Colorability of Composite Resin Molded Article)

In production, the composite resin molded article was molded whileadding a white colorant, and a sensory evaluation was carried out forcolorability such as coloring uniformity and color unevenness. A testpiece showing no color unevenness and uniformly colored into white wasexpressed as “Good”, a test piece showing partial color unevenness at alevel of 1 cm² or smaller in area was expressed as “Middling”, and atest piece showing color unevenness at a level of larger than 1 cm² inarea or showing no white coloring was expressed as “Bad”. The test piecewas able to be colored without color unevenness, and rated as “Good”.

(Appearance of Composite Resin Molded Article)

A sensory evaluation was carried out to determine whether the compositeresin molded article showed fiber aggregates as white spots at a visiblelevel. A composite resin molded article showing no white spot wasexpressed as “Good”, a composite resin molded article showing a whitespot having a long side length of 2 mm or shorter was expressed as“Middling”, and a composite resin molded article showing a white spothaving a long side length of longer than 2 mm was expressed as “Bad”.The test piece showed no white spot, and was rated as “Good”.

EXAMPLE 2

In example 2, a pulp-dispersed polypropylene pellet and a compositeresin molded article were prepared in the same material condition andprocess condition as in example 1 except that a period of pulverizingthe pulp was slightly lengthened. Evaluation was carried out in the samemanner as in example 1.

EXAMPLE 3

In example 3, the pulp was pulverized, then fibers having high aspectratios were removed by a sieve, and only fibers having low aspect ratioswere used. Other material conditions and process conditions were set thesame as in example 1 to prepare a pulp-dispersed polypropylene pelletand a composite resin molded article. Evaluation was carried out in thesame manner as in example 1.

COMPARATIVE EXAMPLE 1

In comparative example 1, a period of pulverizing the pulp wasshortened, and other material conditions and process conditions were setthe same as in example 1 to prepare a pulp-dispersed polypropylenepellet and a composite resin molded article. Evaluation was carried outin the same manner as in example 1.

COMPARATIVE EXAMPLE 2

In comparative example 2, a period of pulverizing the pulp wasconsiderably lengthened, and other material conditions and processconditions were set the same as in example 1 to prepare a pulp-dispersedpolypropylene pellet and a composite resin molded article. Evaluationwas carried out in the same manner as in example 1.

COMPARATIVE EXAMPLE 3

In comparative example 3, a pulp-dispersed polypropylene pellet and acomposite resin molded article were prepared in the same materialcondition and process condition as in example 1 except that the pulp wasnot pulverized. Evaluation was carried out in the same manner as inexample 1.

COMPARATIVE EXAMPLE 4

In comparative example 4, a period of pulverizing the pulp wasconsiderably lengthened, furthermore fibers having high aspect ratioswere removed by a sieve, and only fibers having low aspect ratios wereused. Other material conditions and process conditions were set the sameas in example 1 to prepare a pulp-dispersed polypropylene pellet and acomposite resin molded article. Evaluation was carried out in the samemanner as in example 1.

COMPARATIVE EXAMPLE 5

In comparative example 5, the mold temperature in molding was set to120° C., and the resin was slowly cooled, so that fibers having largeaspect ratios flowed inward. Other material conditions and processconditions were set the same as in example 1 to prepare a pulp-dispersedpolypropylene pellet and a composite resin molded article. Evaluationwas carried out in the same manner as in example 1.

COMPARATIVE EXAMPLE 6

In comparative example 6, the lot of the coniferous pulp was changed toa fiber having low whiteness with lightness of L value of 70. Othermaterial conditions and process conditions were set the same as inexample 1 to prepare a pulp-dispersed polypropylene pellet and acomposite resin molded article. Evaluation was carried out in the samemanner as in example 1.

COMPARATIVE EXAMPLE 7

In comparative example 7, the composite resin molded article wasprepared, then the composite resin molded article was heat-treated atabout 140° C. for about 1 hours to increase a degree of carbonization atthe surface layer side and decrease lightness of L value at the surfacelayer side. Other material conditions and process conditions were setthe same as in example 1 to prepare a pulp-dispersed polypropylenepellet and a composite resin molded article. Evaluation was carried outin the same manner as in example 1.

COMPARATIVE EXAMPLE 8

In comparative example 8, a low shear type kneader was used to preventdefibration of the fibers. Other material conditions and processconditions were set the same as in example 1 to prepare a pulp-dispersedpolypropylene pellet and a composite resin molded article. Evaluationwas carried out in the same manner as in example 1.

The table of FIG. 4 shows measurement results in examples 1 to 3 andcomparative examples 1 to 8.

As apparent from the table of FIG. 4, in example 2 in which the periodof pulverizing the pulp was slightly lengthened, a percentage of thefibers having aspect ratios of 2 or lower was slightly increased to 60to 70%. In example 3 in which the pulp was pulverized, then the fibershaving high aspect ratios were removed by the sieve, and only fibershaving low aspect ratios were used, a percentage of the fibers havingaspect ratios of 10 or higher was decreased to 0 to 5%. In examples 2and 3, the percentage of the fibers having high aspect ratios wasslightly reduced, and thus the elastic modulus was slightly reduced to2.1 GPa, but there was no problem, and it was also confirmed that therewas no problem in impact strength, colorability and appearance. It wasconfirmed that a highly reinforced resin could be obtained as long as anabundance ratio of fibers having aspect ratios of 10 or higher was 1% to10%, an abundance ratio of fibers having aspect ratios of 2 or lower was50% to 70%, a large number of fibers having high aspect ratios of 10 orhigher were charged at the surface layer of the composite resin moldedarticle, and small fibers having aspect ratios of 2 or lower werecharged at the core side of the composite resin molded article.

In comparative example 1 in which the period of pulverizing the pulp wasshortened, pulverization of the fibers did not progress so much, thusthe percentage of the fibers having aspect ratios of 10 or higher was 15to 30%, the percentage of the fibers having aspect ratios of 2 or lowerwas 35 to 45%. As a result, the elastic modulus was slightly increased,but the impact resistance was lowered, and the composite resin moldedarticle was broken in the drop impact test. In addition, white spotswere observed in the composite resin molded article when the fibershaving high aspect ratios aggregated.

In comparative example 2 in which the period of pulverizing the pulp wasconsiderably lengthened, pulverization of the fibers progressed well,the percentage of the fibers having aspect ratios of 10 or higher was 1to 5%, the percentage of the fibers having aspect ratios of 2 or lowerwas 75 to 85%. As a result, the amount of fibers having low aspectratios was increased, and thus the elastic modulus was decreased to 1.8GPa.

In comparative example 3 in which the pulp was not pulverized, thepercentage of the fibers having aspect ratios of 10 or higher was 80 to90%, and the percentage of the fibers having aspect ratios of 2 or lowerwas 0 to 5%. As a result, the elastic modulus was slightly increased,but the impact resistance was lowered, and the composite resin moldedarticle was broken in the drop impact test. In addition, white spotswere observed in the composite resin molded article when the fibershaving high aspect ratios aggregated.

In example 4 in which the period of pulverizing the pulp wasconsiderably lengthened, furthermore the fibers having high aspectratios were removed by a sieve and only fibers having low aspect ratioswere used, the percentage of the fibers having aspect ratios of 10 orhigher was 0%, and the percentage of the fibers having aspect ratios of2 or lower was 80 to 90%. As a result, there were only fibers having lowaspect ratios, and therefore the elastic modulus was significantlydecreased to 1.6 GPa.

In comparative example 5 in which the mold temperature in molding wasset to 120° C., and the resin was slowly cooled so that the fibershaving high aspect ratios flowed inward, the aspect ratios of the fibersin the composite resin molded article were expressed by an equation:aspect ratio at the core side aspect ratio at the surface layer side. Asa result, the elastic modulus was slightly decreased to 2.0 GPa, andalso the impact resistance was slightly deteriorated.

In comparative example 6 in which the lot of the coniferous pulp waschanged to a fiber having low whiteness with lightness of L value of 70,the composite resin molded article was not able to be uniformly coloredbecause of the low whiteness of the fibers, resulting in colorunevenness.

In comparative example 7 in which the composite resin molded article wasprepared, then the composite resin molded article was heat-treated atabout 140° C. for about 1 hours to increase the degree of carbonizationat the surface layer side and decrease lightness of the L value at thesurface layer side, the color difference L values of the resin in thecomposite resin molded article were expressed by an equation: lightnessof L value at the core side lightness of L value at the surface layerside. As a result, the colorability was slightly deteriorated, and atthe same time, the color unevenness due to white spots was also slightlydeteriorated.

In comparative example 8 in which a low shear type kneader was used toprevent defibration of the fibers, the fibers were not defibrated somuch in the composite resin molded article, and there were no fibershaving defibrated end parts. As a result, the elastic modulus wasslightly decreased to 2.0 GPa, and furthermore the impact resistance wasalso slightly deteriorated.

From the above evaluations, an abundance ratio of the fibers havingaspect ratios of 10 or higher is 1% to 10% of the fibers added in thecomposite resin molded body, and an abundance ratio of the fibers havingaspect ratios of 2 or lower is 50% to 70%. A large number of fibershaving high aspect ratios of 10 or higher are charged at the surfacelayer of the composite resin molded article, and fibers having aspectratios of 2 or lower are charged at the core side of the composite resinmolded article, so that both a high elastic modulus and a high impactstrength can be achieved, and furthermore a composite resin moldedarticle having a good appearance without fiber aggregates can beobtained. In addition, a high elastic modulus can be achieved even ifthe aspect ratio is not so high, by preparing a composite resin moldedarticle using a resin material in which only at least one end part ofeach fiber is defibrated. Furthermore, it was found that uniformcolorability could be provided by making lightness of the L value at thesurface layer side higher than lightness of the L value at the core sidein the composite resin molded article using fibers having high whitenesswith a color difference L value of 80 or higher.

Note that the present disclosure includes appropriate combinations ofany embodiments and/or examples from the aforementioned variousembodiments and/or examples, and in the present disclosure, the effectof each embodiment and/or example can be exhibited.

The composite resin molded article according to the present disclosuremakes it possible to provide a composite resin molded article having amechanical strength superior to that of the conventional general-purposeresin. Since the present disclosure makes it possible to improve theproperties of the base resin, the composite resin molded article can beused as an alternative for an engineering plastic or as an alternativefor a metallic material. Consequently, a manufacturing cost for variousindustrial products made of engineering plastics or metals, orlivingwares can be significantly reduced. Furthermore, the compositeresin molded article can be used for home appliance housings, buildingmaterials, and automobile parts.

REFERENCE SIGNS LIST

1 Base resin

2 Fibrous filler (Filler)

3 Particulate filler (Filler)

4 Defibrated part

10 Composite resin molded article

51 Resin

53 Cellulose-based powder

What is claimed is:
 1. A composite resin molded article containing: abase resin; and fillers dispersed in the base resin, wherein the fillersinclude fibrous fillers and particulate fillers having aspect ratioslower than aspect ratios of the fibrous fillers.
 2. The composite resinmolded article according to claim 1, wherein the fibrous fillers haveaspect ratios of 10 or higher, and the particulate fillers have aspectratios of 2 or lower.
 3. The composite resin molded article according toclaim 1, wherein a ratio of the fibrous fillers in the fillers isranging from 1% to 10%, and a ratio of the particulate fillers in thefillers is ranging from 50% to 70%.
 4. The composite resin moldedarticle according to claim 1, wherein a ratio of the fibrous fillers inthe fillers present at a surface layer of the composite resin moldedarticle is higher than a ratio of the fibrous fillers in the fillerspresent at a core side of the composite resin molded article.
 5. Thecomposite resin molded article according to claim 1, wherein the fillershave lightness of L values of higher than 80 determined by a colordifference measurement.
 6. The composite resin molded article accordingto claim 1, wherein the composite resin molded article having lightnessof different L values determined by the color difference measurement ina cross-sectional direction, wherein the lightness of L values at thesurface layer of the composite resin molded article are higher than thelightness of L values at the core side of the composite resin moldedarticle.
 7. The composite resin molded article according to claim 1,wherein at least one end part of each fibrous filler in the compositeresin molded article is defibrated.
 8. The composite resin moldedarticle according to claim 1, wherein the fillers are composed ofnatural fibers.
 9. The composite resin molded article according to claim1, wherein the base resin is composed of an olefin resin.